"paste" disappears before I can select it

I have 2.3.4 installed on my phone, and since I've only had it for a week, I have some very basic questions. Here's one issue that keeps coming up:

When I'm typing in a text box (for ex., on a message board), I sometimes want to paste text (sometimes, I've composed the whole message elsewhere and just need to paste before I post). But, in order to bring up the option for pasting something, I have to hold my finger down on the screen (I'm still quite unclear on the exact technique I'm supposed to follow here) and wait for a box with the option " paste" to pop up. But, at least on some webforums, the instant after "paste" appears as an option, a keyboard pops up and the " paste" option disappears. How do I get it to stay on "paste" for long enough that I can select it?

Also, is there a way I can customize my layout so that "copy", "paste" etc. appear when I press the "menu" button on the bottom row of keys, rather than me having to perform some kind of difficult gymnastics routine on the touch screen?